Production method for improving straightness of groove type steel rail for tramcar

Abstract

The invention relates to a production method for improving the straightness of a groove type steel rail for a tramcar. The production process of the groove type steel rail comprises the steps of vacuum smelting, continuous casting, casting blank heating, high-pressure water descaling, rolling, quenching heat treatment and straightening. The temperature distribution of the trough type steel rail after heat treatment is effectively controlled by reasonably controlling the cooling speed of the railhead of the trough type steel rail and cooperatively adjusting the cooling speed of the rail lip and the rail bottom; by adjusting the process parameters of the subsequent straightening procedure, the produced groove-shaped steel rail has good straightness, and the mechanical property and the straightness of the groove-shaped steel rail both meet the technical requirements of the YB / T4653-2018 standard.

Description

Technical Field

[0001] The invention relates to the technical field of rail production, and in particular to a production method for improving the straightness of a grooved rail for trams. Background Art

[0002] As an energy-saving and environmentally friendly public transportation tool, trams have the characteristics of low construction cost, high safety factor and high running speed. Compared with ordinary buses (including double-decker buses), trams can carry more passengers. At the same time, due to the track system and independent road rights, trams are not easily affected by traffic jams. When the population has not yet reached the scale for building a subway, trams can serve as a good supplement, effectively alleviate urban traffic pressure, promote the development of urban public transportation, and have strategic significance for the rapid development of urbanization and urban construction.

[0003] Tram tracks are laid on the road surface with grooved rails, which have little impact on the road surface and are not affected by running cars. At present, grooved rails used for trams are generally laid directly after hot rolling and are rarely strengthened, so their service life is short. With the rapid increase in tram lines and mileage, the increase in transportation volume and the increase in operating speed, higher requirements are placed on the comprehensive performance of grooved rails such as strength, toughness and straightness. Good straightness can ensure that the tram will not deviate or derail during operation, thereby improving the safety of operation. At the same time, it can make the contact between the wheels and rails of the tram more uniform, thereby reducing the wear of the wheels and rails, effectively extending the service life of the rails, and facilitating maintenance.

[0004] In the actual production process, due to the unique shape of the grooved rail, the amount of metal in the rail head, rail lip and rail bottom is significantly different, and the cooling speed of each part is significantly different, so that after the heat treatment process, there is a significant temperature difference in each part of the cross section of the grooved rail. In the subsequent natural cooling process, due to the effect of thermal stress, the end will bend in different directions and degrees, which significantly affects the subsequent straightening effect and stability. If the straightening process is improper, it will also cause straightening defects in the rail during the straightening process. In severe cases, it may even cause the rail to break during the straightening process, affecting the yield rate of the production line.

[0005] The Chinese patent application with the application number CN 202210889199.2 discloses a "U-shaped steel rail for tram and its preparation method", which includes the following steps: heating the steel billet to a temperature at which the steel billet is easy to roll and deform, and placing it on a blooming mill for blooming rolling; rough rolling, intermediate rolling and finishing rolling the steel billet through a universal rolling mill to form a U-shaped steel rail; inductively heating the whole U-shaped steel rail to a temperature of 750 - 860 °C at the tread of the rail head, and controlling the temperature difference at each part of the surface of the U-shaped steel rail ≤ 30 °C; using a cooling medium to accelerate the cooling of the U-shaped steel rail until the temperature at the tread of the rail head is 400 - 600 °C, controlling the temperature difference at each part of the surface of the U-shaped steel rail ≤ 45 °C, and then naturally cooling to 60 °C; straightening the U-shaped steel rail with a roller straightening machine. By ensuring the straightness of the U-shaped steel rail before heat treatment, during heat treatment and after heat treatment, and then accelerating the cooling of the U-shaped steel rail, high-efficiency production is achieved, and a U-shaped steel rail with excellent anti-fatigue performance and small residual stress of the rail is obtained. However, the same cooling rate is applied to each part of the rail. After the heat treatment is completed, the temperature of the rail head is necessarily higher than that of the rail lip and the rail bottom. During the natural cooling process, due to the different amounts of metal in the rail head, rail lip and rail bottom, the cooling rate of the rail bottom and rail lip is higher than that of the rail head, which will cause the end of the rail to bend to varying degrees under the action of thermal stress, affecting the straightness of the rail.

[0006] The Chinese patent application with the application number CN 202210473796.7 discloses a "U-shaped steel rail with low residual stress and its preparation method". The U-shaped steel rail to be cooled is cooled at a controlled speed to obtain a U-shaped steel rail to be straightened; the U-shaped steel rail to be straightened is straightened to obtain a U-shaped steel rail; wherein, the U-shaped steel rail to be cooled includes a rail head, a rail lip, a rail web and a rail bottom in terms of cross-section, and the controlled-speed cooling includes accelerated cooling, and the accelerated cooling specifically includes: cooling the rail head, rail lip, rail web and rail bottom of the U-shaped steel rail to be cooled at a set cooling rate respectively. This preparation method reduces the residual stress of the whole cross-section of the U-shaped steel rail and improves the uniformity of the residual stress at different positions by adopting corresponding cooling processes for different parts of the cross-section of the U-shaped steel rail. However, it starts controlled cooling after the pearlite phase transformation of the rail is completed, which is not suitable for controlling the straightness of the rail during the heat treatment process.

[0007] The Chinese patent application with the application number CN 201811093074.9 discloses a "Method for Controlling the Straightness of Online Heat Treatment of Steel Rails", which includes the following steps: 1) Bending treatment: After the steel rail is rolled, the hot steel rail is controlled by a bending machine to have a bending degree of 0.4 - 1.0 mm / 1.5 m bending towards the rail bottom; 2) Heat treatment: The accelerated cooling during the heat treatment of the steel rail is divided into two stages. The accelerated cooling time in the first stage is 60 - 100 seconds, and the flow rate ratio of the cooling medium applied to the rail head and the rail bottom is 4 - 7:1; the accelerated cooling time in the second stage is 25 - 50 seconds, and the flow rate ratio of the cooling medium applied to the rail head and the rail bottom is 1:3 - 6; after the heat treatment, the temperature of the rail head is 60 - 120 °C lower than the temperature of the rail bottom. The straightness of the steel rail obtained by this method is 0.9 - 1.2 mm / 1.5 m. However, it is only applicable to ordinary steel rails and not applicable to channel steel rails.

[0008] The Chinese patent application with the application number CN 202110037685.7 discloses a "Production Control Method for Improving the Straightness of Quenched Steel Rails in Online Heat Treatment". Through water mist cooling, the cooling intensity and temperature difference between the rail head and the rail bottom are reasonably controlled, so that the bending of the steel rail after heat treatment is controlled within the ideal range. After the steel rail is cooled, it is straightened with light pressure. The final mechanical properties and straightness of the steel rail meet the technical requirements of the TB / T2344 - 2012 standard. However, it is also only applicable to ordinary steel rails and not applicable to channel steel rails.

[0009] The Chinese patent application with the application number CN 202211110868.8 discloses a "Production Control Method for Improving the Straightness of Quenched Turnout Steel Rails in Online Heat Treatment". A certain cooling rate is applied to each part of the steel rail to keep a certain temperature difference range between each part of the steel rail, so that the steel rail can maintain an ideal straightness both in the heat treatment unit and when leaving the heat treatment unit. The steel rail can also maintain a good straightness when it is slowly cooled to room temperature after leaving the heat treatment unit. By reasonably controlling the cooling intensity and temperature difference of the rail head, rail bottom, left and right ends of the steel rail, the bending of the turnout steel rail after heat treatment is controlled within the ideal range. After the steel rail is cooled, it is straightened with light pressure. The final mechanical properties and straightness of the steel rail meet the technical requirements of the TB / T2344 - 2012 standard. However, the channel steel rail has a more complex cross-sectional shape compared with the turnout steel rail. Not only is the metal amount on both sides of the rail head different, but the difference in the metal amount between the rail head and the rail lip is more obvious. And this method uses water mist cooling, which is likely to cause the cooling rate at the groove of the channel steel rail to be too high to generate martensite when used for channel steel rails. Therefore, this method is also not applicable to channel steel rails. Summary of the Invention

[0010] The present invention provides a production method for improving the straightness of grooved steel rails for tramcars. By reasonably controlling the cooling rate of the rail head of the grooved steel rail and coordinating with the adjustment of the cooling rates of the rail lip and the rail bottom, the temperature distribution after heat treatment of the grooved steel rail is effectively controlled. By adjusting the process parameters of the subsequent straightening process, the produced grooved steel rail has good straightness, and its mechanical properties and straightness both meet the technical requirements of YB / T 4653-2018 standard.

[0011] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0012] A production method for improving the straightness of grooved steel rails for tramcars. The production process of the grooved steel rail includes vacuum smelting, continuous casting, billet heating, high-pressure water descaling, rolling, quenching heat treatment and straightening. Among them, the following processes are controlled:

[0013] 1) Quenching heat treatment;

[0014] After the grooved steel rail is rolled by universal rolling, it enters the quenching heat treatment unit, and compressed air is applied to the rail head, rail lip and rail bottom respectively for forced cooling. The running speed of the conveying roller table is 1.2 - 1.8 m / s. The cooling process is divided into the following two stages:

[0015] The first stage, when the grooved steel rail enters the quenching heat treatment unit, the temperature is 720 - 800 °C. The air spraying cooling method is adopted. The cooling rate of the rail head is 4.0 - 6.0 °C / s, the cooling rate of the rail lip is 40% - 60% of the cooling rate of the rail head, and the cooling rate of the rail bottom is 50% - 70% of the cooling rate of the rail head. When the rail head is cooled to 540 - 600 °C, it enters the second stage;

[0016] The second stage, the grooved steel rail continues to be rapidly cooled by the air spraying cooling method. The cooling rate of the rail head is 2.0 - 4.0 °C / s, the cooling rate of the rail lip is 30% - 50% of the cooling rate of the rail head, and the cooling rate of the rail bottom is 30% - 60% of the cooling rate of the rail head. When the rail head is cooled to 450 - 480 °C, the rail lip is cooled to 530 - 560 °C, and the rail bottom is cooled to 510 - 540 °C, the grooved steel rail exits the quenching heat treatment unit and is naturally cooled in the air;

[0017] 2) Straightening;

[0018] When the grooved steel rail is naturally cooled to 30 - 60 °C, it enters the horizontal-vertical combined straightening unit for straightening, and the straightening speed is 1.6 - 2.2 m / s.

[0019] As a preferred solution, in the straightening process, an 8+1 horizontal and vertical combined straightening machine set is used to straighten the channel steel rails; the 8+1 horizontal and vertical combined straightening machine set is equipped with a total of 9 horizontal rolls from No. 1 horizontal roll to No. 9 horizontal roll, among which the No. 2 horizontal roll, No. 4 horizontal roll, No. 6 horizontal roll and No. 8 horizontal roll are all downward pressure rolls; the straightening process adopts the "large deformation + small deformation" method. The No. 2 horizontal roll and No. 4 horizontal roll adopt large reduction amounts to reduce the original curvature difference of the channel steel rails; the No. 6 horizontal roll and No. 8 horizontal roll adopt small reduction amounts to eliminate the residual curvature; specifically, the reduction amount of the No. 2 horizontal roll is 20-24 mm, the reduction amount of the No. 4 horizontal roll is 13-16 mm, the reduction amount of the No. 6 horizontal roll is 6-10 mm, and the reduction amount of the No. 8 horizontal roll is 3-6 mm.

[0020] After straightening, the vertical curvature of the channel steel rails within 1.5 m from the rail end is ≤0.2 mm, and the straightness meets the requirements of the YB / T4653-2018 standard.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1) By reasonably controlling the cooling rate of the rail head of the channel steel rails and at the same time coordinating the adjustment of the cooling rates of the rail lips and the rail bottom, the present invention effectively controls the temperature distribution of the rails after heat treatment; at the same time, the process parameters of the subsequent straightening process are adjusted, so that the vertical curvature of the channel steel rails for tramways produced within 1.5 m from the rail end is controlled within 0.2 mm, and the mechanical properties and straightness of the channel steel rails meet the technical requirements of the YB / T4653-2018 standard.

[0023] (2) On the basis of improving the straightness of the channel steel rails, the present invention reduces the scrap rate of straightening defects of the channel steel rails, improves the production efficiency of the channel steel rails, enhances the product competitiveness, improves the use safety of the channel steel rails, and has obvious economic and social benefits. Description of the Drawings

[0024] Figure 1 is a schematic cross-sectional view of the channel steel rail described in the present invention.

[0025] In the figure: 1. Rail bottom 2. Rail web 3. Rail head 31. Rail head tread 4. Rail lip 41. Rail lip tread 5. Groove 6. Running edge Specific Embodiments

[0026] The following further describes the specific embodiments of the present invention in conjunction with the drawings:

[0027] Ordinary steel rails are symmetrically structured with a rail bottom, a rail web and a rail head from bottom to top in sequence, and as Figure 1As shown, the U-shaped steel rail has a complex asymmetric cross-section. In addition to the rail base 1 and the web 2, there is a rail lip 4 on one side of the rail head 3. A groove 5 is formed between the rail head 3 and the rail lip 4, and the side of the groove 5 close to the rail head 3 is the running side. The top surface of the rail head 3 is the rail head tread 31, and the top surface of the rail lip 4 is the rail lip tread 41.

[0028] A production method for improving the straightness of U-shaped steel rails for tramways according to the present invention. The production process of the U-shaped steel rail includes vacuum smelting, continuous casting, billet heating, high-pressure water descaling, rolling, quenching heat treatment, and straightening. Among them, the following processes are controlled:

[0029] 1) Quenching heat treatment;

[0030] After the U-shaped steel rail is rolled by universal rolling, it enters the quenching heat treatment unit, and compressed air is applied to the rail head, rail lip, and rail base respectively for forced cooling. The running speed of the conveying roller table is 1.2 - 1.8 m / s. The cooling process is divided into the following two stages:

[0031] The first stage: When the U-shaped steel rail enters the quenching heat treatment unit, the temperature is 720 - 800 °C. The air spraying cooling method is adopted. The cooling speed of the rail head is 4.0 - 6.0 °C / s, the cooling speed of the rail lip is 40% - 60% of the cooling speed of the rail head, and the cooling speed of the rail base is 50% - 70% of the cooling speed of the rail head. When the rail head is cooled to 540 - 600 °C, it enters the second stage. The main purpose of this stage is to apply rapid cooling to the rail head of the U-shaped steel rail to obtain a fine pearlite structure, thereby improving the mechanical properties of the U-shaped steel rail. At the same time, different cooling speeds are applied to other parts to control the temperature distribution of the U-shaped steel rail, so as to control the temperature of each part of the U-shaped steel rail in the second stage. If the cooling speed is too fast, abnormal structures such as martensite will appear; if the cooling speed is too slow, the pearlite structure will be coarse, affecting the heat treatment effect.

[0032] The second stage: The U-shaped steel rail continues to be rapidly cooled by the air spraying cooling method. The cooling speed of the rail head is 2.0 - 4.0 °C / s, the cooling speed of the rail lip is 30% - 50% of the cooling speed of the rail head, and the cooling speed of the rail base is 30% - 60% of the cooling speed of the rail head. When the rail head is cooled to 450 - 480 °C, the rail lip is cooled to 530 - 560 °C, and the rail base is cooled to 510 - 540 °C, the U-shaped steel rail exits the quenching heat treatment unit and is naturally cooled in the air. The main purpose of this stage is to control the surface reheat caused by the temperature difference between the surface and the core of the steel rail after rapid cooling in the first stage. At the same time, different cooling speeds are continuously applied to each part of the U-shaped steel rail to effectively control the temperature distribution of the U-shaped steel rail after heat treatment.

[0033] The U-shaped steel rail after quenching heat treatment basically remains straight or is slightly bent in the vertical direction, meeting the conditions for entering the straightening unit.

[0034] 2) Straightening;

[0035] When the channel steel rail is naturally cooled to 30 - 60 °C, it enters the combined horizontal and vertical straightening machine set for straightening, and the straightening speed is 1.6 - 2.2 m / s.

[0036] As an optimized solution, in the straightening process, an 8 + 1 combined horizontal and vertical straightening machine set is used to straighten the channel steel rail; the 8 + 1 combined horizontal and vertical straightening machine set is equipped with a total of 9 horizontal rolls from No. 1 horizontal roll to No. 9 horizontal roll, among which No. 2 horizontal roll, No. 4 horizontal roll, No. 6 horizontal roll and No. 8 horizontal roll are all downward pressure rolls; the straightening process adopts the "large deformation + small deformation" method, and the "large deformation + small deformation" method means that: No. 2 horizontal roll and No. 4 horizontal roll adopt large reduction amounts to eliminate the differences in the original curvature of different degrees before straightening of the channel steel rail; No. 6 horizontal roll and No. 8 horizontal roll adopt small reduction amounts to eliminate the residual curvature. After straightening in this way, the channel steel rail has good flatness, and the residual stress at the rail bottom meets the standard requirements. Specifically, the reduction amount of No. 2 horizontal roll is 20 - 24 mm, the reduction amount of No. 4 horizontal roll is 13 - 16 mm, the reduction amount of No. 6 horizontal roll is 6 - 10 mm, and the reduction amount of No. 8 horizontal roll is 3 - 6 mm.

[0037] The bending degree of the straightened channel steel rail in the vertical direction within 1.5 m from the rail end is ≤ 0.2 mm, and the flatness meets the standard requirements of YB / T4653 - 2018.

[0038] In order to more intuitively reflect the present invention, the implementation manners of the present invention will be further described in combination with embodiments. The following embodiments are only the preferred specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solutions that can be obtained obviously by those skilled in the art within the technical scope disclosed by the present invention, including simple changes or equivalent replacements, are all within the protection scope of the present invention.

[0039]

Embodiment

[0040] This embodiment uses the production method described in the present invention to produce channel steel rails with a specification of 60R2 and a material of U75V. The production process includes vacuum smelting, continuous casting, billet heating, high-pressure water descaling, rolling, quenching heat treatment and straightening.

[0041] In each embodiment and comparative example, the heat treatment process parameters of the channel steel rail are shown in Table 1, the straightening process parameters are shown in Table 2, and the microstructure and properties of the finished channel steel rail are shown in Table 3.

[0042] Table 1 Main heat treatment process parameters in each embodiment and comparative example

[0043]

[0044] Table 2 Straightening process parameters in each embodiment and comparative example

[0045]

[0046] Table 3 Microstructure and properties of finished U-shaped steel rails in each example and comparative example

[0047]

[0048] As can be seen from Table 3, the performance indicators and microstructure of the U-shaped steel rails prepared in Examples 1-4 are good and meet the technical requirements of the YB / T 4653-2018 standard; compared with the U-shaped steel rails prepared in Comparative Example 1, the method of the present invention can effectively improve the flatness of the U-shaped steel rails on the premise of ensuring qualified microstructure and mechanical properties.

[0049] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered by the protection scope of the present invention.

Claims

1. A production method for improving the straightness of grooved steel rails for tramcars, characterized in that, The production process of the channel steel rail includes vacuum smelting, continuous casting, billet heating, high-pressure water descaling, rolling, quenching heat treatment and straightening; among which, the following processes are controlled: 1) Quenching heat treatment; After universal rolling, the channel steel rail enters the quenching heat treatment unit, and compressed air is applied to the rail head, rail lip and rail bottom respectively for forced cooling. The running speed of the conveying roller table is 1.2 - 1.8 m / s; the cooling process is divided into the following two stages: In the first stage, when the channel steel rail enters the quenching heat treatment unit, the temperature is 720 - 800 °C. The air spraying cooling method is adopted. The cooling speed of the rail head is 4.0 - 6.0 °C / s, the cooling speed of the rail lip is 40% - 60% of the cooling speed of the rail head, and the cooling speed of the rail bottom is 50% - 70% of the cooling speed of the rail head; when the rail head is cooled to 540 - 600 °C, it enters the second stage. In the second stage, the channel steel rail continues to be rapidly cooled by the air spraying cooling method. The cooling speed of the rail head is 2.0 - 4.0 °C / s, the cooling speed of the rail lip is 30% - 50% of the cooling speed of the rail head, and the cooling speed of the rail bottom is 30% - 60% of the cooling speed of the rail head; when the rail head is cooled to 450 - 480 °C, the rail lip is cooled to 530 - 560 °C, and the rail bottom is cooled to 510 - 540 °C, the channel steel rail exits the quenching heat treatment unit and is naturally cooled in the air. 2) Straightening; When the channel steel rail is naturally cooled to 30 - 60 °C, it enters the horizontal-vertical combined straightening unit for straightening, and the straightening speed is 1.6 - 2.2 m / s.

2. The production method for improving the straightness of grooved steel rails for tramcars according to claim 1, characterized in that, In the straightening process, an 8 + 1 horizontal-vertical combined straightening unit is used to straighten the channel steel rail; the 8 + 1 horizontal-vertical combined straightening unit is equipped with a total of 9 horizontal rolls from 1# horizontal roll to 9# horizontal roll, among which the 2# horizontal roll, 4# horizontal roll, 6# horizontal roll and 8# horizontal roll are all downward pressure rolls; the straightening process adopts the "large deformation + small deformation" method. The 2# horizontal roll and 4# horizontal roll adopt large reduction amounts to reduce the original curvature difference of the channel steel rail; the 6# horizontal roll and 8# horizontal roll adopt small reduction amounts to eliminate the residual curvature; specifically, the reduction amount of the 2# horizontal roll is 20 - 24 mm, the reduction amount of the 4# horizontal roll is 13 - 16 mm, the reduction amount of the 6# horizontal roll is 6 - 10 mm, and the reduction amount of the 8# horizontal roll is 3 - 6 mm.

3. A production method for improving the straightness of grooved steel rails for tramcars according to claim 1, characterized in that, After straightening, the vertical bending degree within 1.5 m from the rail end of the channel steel rail ≤ 0.2 mm, and the straightness meets the requirements of the YB / T4653 - 2018 standard.

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